Personally, I'm a firm believer in sitting back, watching and giving someone enough rope. If it was me and I was unsure, I would order a few motion activated nanny cams. Then instead of hiding things I would put stuff out and buy some new things like a jewelry box, maybe a couple storage bins or anything that a thief might find tempting to go through. Then sit back and watch. If she goes through everything, then you know you don't want her around.
If that ends up happening, warn anyone else that you have them set up for the kids to keep them honest.
HDH